Fluidized bed heat exchanger

ABSTRACT

A fluidized bed heat exchanger and a method of controlling same in which a first chamber and plurality of additional chambers are formed in a housing. A particulate material is supported in all of the additional chambers and air is introduced to each of the additional chambers to fluidize the material. Particulate material is introduced into one of the chambers and the chambers communicate to permit the material to flow between the chambers. Heat is extracted from one or more of the other additional chambers and the material upon exceeding a predetermined height flows from the other additional chambers to the first chamber before discharging via the first chamber externally of the housing.

This is a continuation of copending application Ser. No. 135,814, filedon Dec. 21, 1987 now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to a fluidized bed heat exchanger and a method ofoperating same in which heat is transferred from hot particulatematerial which flows through a plurality of chambers.

Various types of reactors, or heat exchangers, such as steam generators,or the like, utilize a fluidized bed as the primary medium of heattransfer. In these arrangements, air is passed through a bed ofparticulate material to fluidize the bed.

The most typical fluidized bed system is commonly referred to as a"bubbling" fluidized bed in which a bed of particulate materials issupported by an air distribution plate, to which air is introducedthrough a plurality of openings in the plate, causing the material toexpand and to take on a suspended, or fluidized, state. The gas velocityis typically two to three times that needed to develop a pressure dropwhich will support the bed weight (e.g., minimum fluidization velocity),causing the formation of bubbles that rise up through the bed and giveit the appearance of a boiling liquid. The bed exhibits a well-definedupper surface, and the entrainment of particles in the gas leaving thebed is quite low, such that collection and recycle of these particles isnot always necessary. The heat and mass transfer properties of thetwo-phase mixture are high, being typical of a liquid.

In these type arrangements, heat exchange surfaces are often immersed inthe bed of fluidized particulate material to remove heat from thematerial and utilize the heat for other purposes. When such an immersedheat exchanger is used, it is often desirable to be able to control therate at which the heat is extracted. This is usually done by varying thefluidized bed height and therefore the quantity of surface that isimmersed.

However, situations exist in which a sufficient degree of freedom inchoosing bed height is not available, such as for example, when aminimum fluidized bed solids depth or pressure is required for reasonsunrelated to heat transfer. In this case, the heat transfer may becontrolled by diverting a portion of the particulate material so it doesnot contact and become cooled by the heat exchanger. When the correctportions of cooled and uncooled material are subsequently recombined,the desired final material temperature may be obtained. For example,different type valves, such as "plug valves" and "L valves," have beenused to bleed a portion of the solids passing through the bed and/or todirectly control the flow rates from both a heat exchanger bed and amaterial-pressure control bed. However, these type arrangements requirethe use of moving parts within the solids system and/or need solids flowconduits with associated aeration equipment.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide afluidized bed heat exchanger and method of operating same in which theamount of heat extracted from the fluidized bed is controlled withouthaving to vary the quantity of heat exchange surface that is immersed inthe fluidized bed.

It is a further object of the present invention to provide a heatexchanger and method of the above type in which the heat extraction rateis controlled by diverting a portion or all of the materials from theheat exchanger without the problems normally associated therewith.

It is a still further object of the present invention to provide a heatexchanger and method of the above type in which the rate of heatextracted from the fluidized bed is controlled by bypassing a portion orall of the particulate material away from the heat exchanger andsubsequently recombining it with the portion in contact with the heatexchanger.

It is a still further object of the present invention to provide a heatexchanger and method of the above type in which a plurality of separatefluidized beds are provided within the heat exchanger vessel, one ormore of which is provided with heat exchange surface and the others ofwhich are used to control the quantity of the particulate materialexposed to the heat exchange surface.

Toward the fulfillment of these and other objects, a first chamber (thesolids discharge chamber) and a plurality of additional chambers areprovided in a housing and particulate material is introduced to one ofthe additional chambers and permitted to flow to the other additionalchambers. Heat exchange surface is provided in one or more of theadditional chambers for extracting heat from the fluidized bed therein,and the material in the additional chambers are permitted to flow intothe first chamber when the level in the additional chambers exceeds apredetermined height. Material entering the first chamber is dischargedfrom the housing to external equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

The above brief description, as well as further objects, features andadvantages of the present invention will be more fully appreciated byreference to the following detailed description of the presentlypreferred but nonetheless illustrative embodiments in accordance withthe present invention when taken in conjunction with the accompanyingdrawings wherein:

FIG. 1 is a sectional view of the fluidized bed reactor of the presentinvention;

FIG. 2 is a cross-sectional view taken along the line 2--2 of FIG. 1;

FIG. 3 is a top plan view of the reactor of FIG. 1,; and

FIG. 4 is an enlarged, partial, perspective view depicting thepartitions utilized in the reactor of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1-4 of the drawings, the reference numeral 10 refersin general to the reactor of the present invention which includes avessel, or housing, formed by a front wall 12, a rear wall 14, and twoside walls 16 and 18 (FIG. 2). An outlet opening 20 is provided in theupper portion of the wall 14 for permitting gases to pass from thereactor, as will be explained.

A pair of spaced, parallel partitions 22 and 24 extend between the sidewalls 16 and 18, and a partition 26 (FIGS. 2 and 3) extends between thepartitions 22 and 24 to divide the housing into four chambers, A, B, C,and D. Chamber D extends immediately behind chamber A, and chambers Band C extend to the sides of chambers A and B as better shown in FIG. 3.

An air distributor 30 extends horizontally in the lower portion of thehousing between the walls 12 to 22, 24 to 14, and from the sidewall 16to the partition 26.

An air conduit 31 is disposed below the lower end of the housing andcommunicates with three ducts 32a, 32b and 32c which distribute air intothree plenums 34a, 34b and 34c disposed immediately below the airdistributor 30 below the chambers A, B and C, respectively.

Control valves 36a, 36b and 36c are disposed in the conduits 32a, 32band 32c, respectively, to control the flow of air from the conduit 30into the air plenums 34a, 34b and 34c and therefore into the chambers A,B, and C, respectively.

A hot particulate material inlet pipe 40 extends from an external source(not shown) into and through chamber A, with its outlet end portionextending just above the air distributor 30. Particulate material canthus be continuously fed into chamber A via the conduit 40. It isunderstood that an additional particulate material can be introduced tothe chamber A in a similar manner via the conduit 40 or, alternately,via another feeder (not shown).

As better shown in FIG. 4, the lower portions of those portions of thepartitions 22 and 24 defining the chamber A have openings, or notches42a and 42b, respectively, formed therethrough to permit the hotparticulate material to flow from the chamber A into the chambers B andC.

A pair of weir-type openings 44a and 44b are provided in those portionsof the partitions 22 and 24 which define the chamber D to permit theparticulate material in the chambers B and C to overflow into thechamber D when the buildup of particulate materials in chambers B and Cexceeds a predetermined height. A hopper portion 46 is provided in thelower portion of the chamber D which communicates with an outlet conduit48 for permitting the hot particulate fuel material in the chamber D toexit from the reactor.

A heat exchanger, shown in general by the reference numeral 50, isdisposed in the chamber B and consists of one or more tube bundles, onetube of which is shown by the reference numeral 50. Each heat exchangerbundle 50 has an inlet 50a connected to a source of cooling fluid, suchas water or steam, and an outlet 50b for passing the fluid to externalequipment after the fluid has passed through the chamber B and thusextracted heat from the fluidized bed in the latter chamber.

In operation, hot particulate material is introduced into the chamber Avia the inlet conduit 40, it being understood that additional materialcan also be introduced into the chamber in a similar manner. The airdampers 36a, 36b and 36c are opened as desired to permit fluidizing airto pass upwardly through the air plenums 34a, 34b and 34c and throughthe air distributor 30 and into the chambers A, B and C, respectively.The air thus fluidizes the particulate material in the chambers A, B &C, with the velocity of the air and therefore the degree of fluidizationand the resultant height of the material in the chambers beingcontrolled as needed by varying the position of the dampers 36a, 36b and36c. The particulate material accumulating in the chamber A passesthrough the openings 42a and 42b in the partitions 22 and 24respectively, and into the chambers B and C, respectively.

The fluidizing air for chambers A, B, and C passes to the upper portionsof the chambers A, B, and C where it exits through the outlet 20. Theparticulate material builds up in chambers A, B and C and, when theheight of the material exceeds the height of the weir openings 44a and44b, the material will overflow into the chamber D and exit via theoutlet 48.

The velocity of the air entering the chamber A is controlled by thedamper 36a to fluidize the particulate material in the bed at a valuethat is considered to be optimum for providing a pressure seal for theconduit 40. The air velocity entering the beds in the chambers B and Cis controlled by the dampers 36b and 36c according to heat transfercontrol requirements. Since the fluidizing velocity in the chambers Band C will usually be different from that in chamber A, the material inthe chambers B and C will have different densities. Since theparticulate material communicates between the chambers A and B andbetween the chambers A and C through the openings 42a and 42b, the bedswill operate at different heights. The exit weirs 44a and 44b willtherefore discharge quantities of material from the chambers B and C,respectively, into the chamber D that depend upon the expanded bedheights attained in chambers B and C. In this manner, the fraction ofthe total material flow that passes through the chambers B and C iscontrolled by varying the fluidized velocities in the latter beds.

It is thus seen that several advantages result from the foregoing. Forexample, the heat extraction rate from the fluidized bed in the chamberB is controlled by varying the air velocity in the chambers B and C.Also, the reactor of the present invention can be easily started upsince there is an uncooled flow path for the particulate material duringstartup. Also, the solids exit from the reactor of the present inventionvia the conduit 48 while avoiding backflow or backsplashing. Further, asufficient height of particulate material in the chamber A is assured toprovide a pressure seal for the inlet conduit 40. Also, the mass ofmaterial contained in the beds provides a buffer aginst flow transientsand/or pressure transients.

A latitude of modification, change and substitution is intended in theforegoing disclosure and in some instances some features of theinvention will be employed without a corresponding use of otherfeatures. Accordingly, it is appropriate that the appended claims beconstrued broadly and in a manner consistent with the scope of theinvention.

What is claimed is:
 1. A fluidized bed heat exchanger comprising ahousing; partition means formed in said housing to divide said housinginto an inlet chamber, an outlet chamber sharing a common wall with saidinlet chamber and two additional chambers respectively extending alongthe sides of, and sharing common walls with, said inlet and outletchambers; means for introducing particulate material to said inletchamber; first means for permitting said material to flow simultaneouslyfrom said inlet chamber to both of said additional chambers; heatexchange means disposed in at least one of said additional chambers forremoving heat from said material in said at least one additionalchamber; second means for permitting said material to flow from saidadditional chambers to said outlet chamber; means for introducing air toat least one of said chambers to fluidize the material therein; andmeans for discharging said material from said outlet chamber.
 2. Theheat exchanger of claim 1 wherein the second-permitting means is capableof permitting said material to flow simultaneously from said additionalchambers to said outlet chamber.
 3. The heat exchanger of claim 1wherein said air introducing means comprises means for introducing airto said inlet chamber and said additional chambers to fluidize theparticulate material therein.
 4. The heat exchanger of claim 3 whereinsaid air introducing means comprises an air plenum extending below saidinlet chamber and said additional chambers for receiving fluidizing air,and an air distributor extending above said air plenum for supportingsaid material and distributing air from said plenum through saidmaterial in said inlet chamber and said additional chambers.
 5. The heatexchanger of claim 1 wherein said first means for permitting thematerial to flow from said inlet chamber to said additional chamberscomprises openings formed in said partition means.
 6. The heat exchangerof claim 1 wherein said second means for permitting the material to flowfrom said additional chambers to said outlet chamber comprises weirsformed in said partition means so that said material flows from saidadditional chambers to said outlet chamber in response to the height ofsaid material in said additional chambers exceeding a predeterminedvalue.